Modern commercial buildings must discard significant quantities of waste heat during their occupied cycle in cold weather. During nights and week-ends however, there is a reversal in which heat must be imported to maintain temperature.
Thermal storage can provide a means of enhancing energy conservation when applied to buildings with significant interior heating gain, some of which may be solar originated. Thermal storage systems can effect savings in fuel, electric cooling demands and electric utility investment.
Although thermal storage tanks may be constructed of non-corrosive steel, the cost for large tanks of such material is generally prohibitive. The material generally used in the construction of thermal storage tanks has been concrete and in using concrete there has been a tendency to incorporate thermal storage tanks as part of the structural elements in a building which necessitates co-operative design between the architect, structural engineer and mechanical engineer. Notwithstanding, and despite additional costs to include waterproofing coating membranes, concrete tanks for thermal storage purposes do not have a good record against leakage. Many leaks can be fixed but are generally unsightly and leaks always raise concern of having an effect on the structural aspects of the building including possible soil erosion and building settlement. Often the leaks occur in the vicinity of the side inlet and outlet pipes and if pump rooms are in the proximate area, leakage could partially flood such rooms.
Accordingly thermal storage tanks should preferably not be designed as part of the structural elements in buildings and the conduit connections with the tank should be associated where possible with the top of the tank, not the sides or bottom.
Further, one of the major problems encountered in thermal storage systems is the temperature blending of water. Although there may be cases where blending exacts no penalty (or is even desirable), there are many situations where blending can nullify the benefits of thermal storage. At temperatures in the 5.degree. to 15.degree. C. range, there is little difference in the buoyancy of water and there is a tendency for thermal tanks to destratify with any turbulence at the inlet or outlet of the storage tank. Temperature blending reduces the value of storage by debilitating the prime temperature which may be necessary to fulfill results in simple systems.
There are a number of concepts that have been developed to control or eliminate temperature blending of water in thermal storage systems and maintain separation between the prime water temperature and that returning from the building system.
Canadian Pat. No. 1,038,176 granted Sept. 12, 1978 and its corresponding U.S. Pat. No. 4,135,571 granted Jan. 23, 1979 relate to thermal storage systems and in particular show in one embodiment a movable or floatable tank diaphragm or membrane and show in other embodiments solid separation of a storage tank by a vertical baffle and associated pulley mechanism.
Even with diaphragms or membranes moving in an up-down mode, some problems arise because the membrane has a tendency not to settle uniformly against the bottom of the tank, partly due often to the membrane gravitating or migrating toward the outlet pipe from which water is being withdrawn. Accordingly there has been a tendency to add additional structural elements within a tank and exterior thereto to protect the membrane and reduce the chances of it being damaged.
Membranes also tend to move haphazardly within the tank and even when suitably attached to the walls of the tank to move in an up-down mode rather than from side-to-side, there is not a clear demarcation of different temperatured zones. Haphazard movement of the membrane, which fail to maintain the "platform" of the membrane in a horizontal plane, also tends to shed the insulating film which develops above and below the horizontal element, thus increasing transfer of heat from warmer water above to stored cold water below. Side panels in the membrane also provide areas where heat transfer could disadvantageously take place.
The vertical orientated baffle has a tendency to move in a stepwise fashion or on a slant providing for possible unwanted slippage of water past the membrane.
The present invention seeks to provide a thermal storage tank for use in air conditioning/heating systems which is relatively simple to construct, does not form part of the structural elements of the building and which has means to prevent blending of different temperatured water in the form of a disc which moves upwardly and downwardly within a tank having constant cross-section, the demarcation of the different temperatured water being therefore substantially horizontal at all times. The floating disc assures horizontality of the temperature separation, minimizing heat transfer. Lacking the side panels of the membrane it also benefits from reduced heat transfer through those elements of the membrane and slippage of water between chambers is maintained to a minimum.